TASC Biology Level 3 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cell theory

All organisms are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells through division.

Prokaryote vs eukaryote

Prokaryotes lack a membrane-bound nucleus and organelles, while eukaryotes have a nucleus and membrane-bound structures such as mitochondria and chloroplasts.

Osmosis

The diffusion of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration until balance is reached.

Enzyme active site

The region of an enzyme where the substrate binds; its shape is specific to the substrate, and temperature or pH changes can alter that shape and reduce activity.

ATP function

ATP is the main energy-carrying molecule of cells; breaking its terminal phosphate bond releases energy that powers cellular work such as transport and synthesis.

Mendel's law of segregation

Two alleles for a trait separate during gamete formation, so each gamete receives only one allele and offspring regain two at fertilization.

Genotype versus phenotype

Genotype is the pair of alleles an organism carries, while phenotype is the observable trait that results from that genotype and environmental influence.

Test cross purpose

Crossing an individual showing a dominant trait with a homozygous recessive individual reveals whether the dominant parent is homozygous or heterozygous.

Codominance

Both alleles are expressed fully in the heterozygote, producing a phenotype showing both traits at once, as in human AB blood type.

X-linked recessive trait

A trait controlled by a recessive allele on the X chromosome; it appears more often in males, who carry only one X chromosome.

Frameshift mutation

An insertion or deletion of nucleotides not in multiples of three shifts the reading frame, usually changing every downstream amino acid in the protein.

Natural selection

Heritable variation plus differential reproductive success under environmental pressure causes favorable traits to become more common in a population over generations.

Genetic drift

Random change in allele frequencies from generation to generation, strongest in small populations, as in bottleneck and founder events.

Homologous structures

Body parts in different species that share common ancestry but may serve different functions, such as a human arm and a bat wing.

Reproductive isolation

A condition in which populations can no longer interbreed to produce fertile offspring, which allows them to diverge into separate species.

Binomial nomenclature

A two-part Latin naming system giving each species a genus name and a species name, both italicized with the genus capitalized.

Logistic growth

Population growth that slows as density rises and levels off at carrying capacity, producing an S-shaped curve limited by resources.

Carrying capacity

The maximum population size an environment can sustain indefinitely given available food, water, space, and other limiting resources.

Negative feedback

A control mechanism in which a change from the set point triggers a response that reverses the change, restoring stability such as normal body temperature.

Mark-recapture estimate

A method estimating population size by multiplying the number marked in the first sample by the total in the second, then dividing by recaptured marked individuals.

Survivorship curve types

Type I shows high survival early and rapid late decline, Type II shows constant mortality, and Type III shows high early mortality with few survivors.

Trophic energy transfer

Only about ten percent of energy at one trophic level passes to the next; the rest is lost mainly as heat through metabolism.

Primary succession

Colonization of lifeless surfaces such as bare rock or lava, beginning with pioneer species like lichens that help build soil over time.

Biomagnification

The increasing concentration of a persistent substance, such as a pollutant, in organisms at successively higher trophic levels of a food chain.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by bacteria, making nitrogen available to plants for building proteins and nucleic acids.

Invasive species impact

A nonnative species spreading rapidly without natural predators or controls, often outcompeting native species and disrupting established food webs.

Hypothesis versus theory

A hypothesis is a testable, falsifiable prediction, while a theory is a broad explanation supported by extensive repeated evidence.

Independent variable

The factor the researcher deliberately changes or manipulates between groups in an experiment to observe its effect.

Control group role

A group that receives no treatment or an inactive placebo, providing a baseline for comparison so the treatment effect can be isolated.

Total magnification

The product of the ocular lens power and the objective lens power; a 10x ocular with a 40x objective gives 400x magnification.

Correlation versus causation

Two variables changing together does not prove one causes the other; a confounding factor may explain the observed relationship.

Metric prefixes

Kilo means 1000, centi means one hundredth, and milli means one thousandth, so 1 meter equals 100 centimeters and 1000 millimeters.